Coca-Cola is to launch a naturally sweetened drink in green cans as its response to an official anti-obesity drive. Photograph: Coca-Cola/PA

Coca-Cola has announced plans to launch a new version of its bestselling soft drink with a third less sugar and a third fewer calories as part of government and industry efforts to tackle obesity.

Coca-Cola Life, first piloted in Argentina and Chile last year, is sweetened from natural ingredients rather than artificial sweeteners and will launch in the UK in the autumn. It is the first new Coca-Cola to be launched in the UK since the arrival of Coca-Cola Zero in 2006, a low-calorie version targeted at men.

The company said the new drink would help meet its pledges made under the UK government's voluntary anti-obesity drive – the responsibility deal – and would offer consumers a greater choice.

But health campaigners said the company was misleading shoppers as the new product was still laden with sugar – more than four teaspoons of sugar per 330ml can – equivalent to one quarter of a child's daily recommended maximum intake.

Sweetened with a blend of sugar and naturally sourced stevia leaf extract, a 330ml can of Coca-Cola Life contains 89 calories and will feature striking green branding that will contrast with the familiar red packaging. A can of standard Coca-Cola contains 139 calories.

An extract from the stevia plant, which is native to South America, is already used in the company's Sprite and Glacéau vitamin water, as well as by other manufacturers.

In the UK, Cola-Cola is a signatory to the government's controversial responsibility deal, which aims to improve public health, and has committed the company to reduce the average calories per litre in its range of sparkling drinks by 5% by the end of 2014. More than 40% of the cola sold by Coca-Cola in the UK is already no-calorie, it says, including two zero-calorie options – Coca-Cola Zero and Diet Coke.

Dr Aseem Malhotra, scientific director of Action on Sugar, set up earlier this year to reduce the amount of sugar added to food and soft drinks, said: "Whatever the company says, this is a product with a high sugar content and it will encourage people to have a sweet tooth. Companies like Coca-Cola have no interest whatsoever in public health."

The Children's Food Campaign said : "In light of recent calls for a sugary drinks duty, the new Action on Sugar campaign and the chief medical officer openly considering the need for a sugar tax, we are now seeing industry trying to appear as though they are responding.

"Fundamentally, this is about a company launching a sugary product to encourage more people to consume a substance that contributes to a range of dietary and health-related problems, including diabetes. Coca-Cola appears to be using the cover of the government's discredited responsibility deal to seek acclaim for bringing out a product that still contains over 4 teaspoons of sugar per 330ml can, which equates to one-quarter of a child's daily recommended maximum intake of sugar."

It said the nature of Coca-Cola's business, of selling the public sugar products, had not changed: "There is no commitment to stop promoting or selling their full-sugar brands, or of 'smart-swapping' to diet and no-sugar alternatives, as Public Health England recommends."

James Quincey, president of Coca-Cola Europe, said: "We were early signatories to the UK government's responsibility deal and, as we work with others across society to address the public health challenge of obesity in the UK and across Europe, we will continue to take actions that help people balance their lifestyles."